1. Field of the Invention
The present invention relates to an active matrix type display device in which a pixel circuit is formed using a plurality of thin film transistors, and a method of manufacturing the display device.
2. Description of the Related Art
As a flat panel display, a display device in which an organic EL element using electroluminescence of an organic material is provided for each pixel has been attracting attention. This display device, that is, the organic EL display has excellent features of a wide viewing angle, low power consumption and the like because the organic EL display uses a light emitting phenomenon of organic EL elements themselves. In addition, because the organic EL display makes fast response to a high-definition high-speed video signal, development has been underway to put the organic EL display to practical use particularly in a video field and the like.
Of driving systems of the organic EL display, an active matrix system in which a driving pixel circuit is provided for an organic EL element of each pixel excels an existing passive matrix system in response time and resolution. Thus, the active matrix system is considered to be a driving system capable of fully bringing out features of organic EL elements.
The above-described pixel circuit is formed using thin film transistors (TFTs). Because the organic EL element in particular is a current-driven element, variations in current due to characteristic variations and deterioration of the thin-film transistors forming the pixel circuit in an organic EL display using the organic EL element directly lead to degradation in picture quality. Accordingly, a constitution in an active matrix type organic EL display has been proposed which constitution corrects the characteristic variations of the thin-film transistors by devising a pixel circuit (see Japanese Patent Laid-Open No. 2003-255856).
Another example of the flat panel display is an active matrix type liquid crystal display device. In this liquid crystal display device, a constitution has been proposed in which, for light resistance, an active element (thin film transistor) of a pixel part is formed by amorphous silicon or crystalline silicon, and an active element of a peripheral driving circuit is formed by single-crystal silicon (see Japanese Patent Laid-Open No. Sho 64-2088).